Diabetes is supposed to be one of the causes of retinopathy. At present, some antidiabetics which reduce the blood glucose level are used clinically; however, none of them is effective as treating agents for retinopathy. Therefore, it is thought that there is no correlation between the reduction in the blood glucose level and the treatment and prevention of retinopathy.
As the causes of retinopathy, impediment of blood stream in retinal vessels is suggested, as reported in Eur. J. clin. Invest., 13, 231, 1983. This impediment is supposed to be caused by aggregation of blood, and hence, inhibition of whole blood aggregation is supposed to have some correlation with the treatment and prevention of retinopathy.
It is known that 2-(2-phenyl-2-(2-pyridyl))ethyl-2-imidazoline reduces the blood glucose level and inhibits platelet aggregation and is useful as a antidiabetic agent, as disclosed in U.S. Pat. No. 4,138,491. However, as is apparent from the above description, the former activity of this compound does not suggest the application of this compound to the treatment and prevention of retinopathy.
Also, the latter activity of this compound does not suggest the application of this compound to the treatment and prevention of retinopathy. This is apparent from literature reference (Doumyaku Kouka 12, 1, 139-143, (1984)) which discloses that sensitivity of platelet aggregation in diabetic patients is the same as that in normal persons. However, this literature reference discloses that sensitivity of whole blood aggregation in diabetic patients is higher than that in normal persons.
Investigation had been made to find out the compound which inhibits the whole blood aggregation, and the present inventors found that the above-described compound has the activity for inhibiting the whole blood aggregation. Moreover, it was confirmed by clinical trial that the above compound was clinically useful for the treatment and prevention of retinopathy.